Carrier employing snap-fitted membrane retainer

ABSTRACT

Disclosed herein is an improved carrier design for use in a chemical mechanical polishing process. The carrier employs a retainer ring that is fastened to the side of carrier, as opposed to the front of the carrier, which alleviates undesired uneven wear of the retainer ring surface. Specifically exemplified herein is a carrier comprising a membrane that is secured to the carrier body by a retainer ring that is snap-fitted to the carrier body.

Conventional chemical/mechanical polishing (CMP) has been developed for providing smooth topographies of the various layers formed during semiconductor device manufacture. The CMP process involves holding, and rotating, a thin, reasonably flat, semiconductor wafer against a rotating polishing platen. The wafer may be repositioned radially within a set range on the polishing platen as the platen is rotated. The polishing surface, which is conventionally an open-celled, polyurethane pad affixed to the polishing platen, is wetted by a chemical slurry, under controlled chemical, pressure, and temperature conditions. The chemical slurry contains selected chemicals which etch or oxidize selected surfaces of the wafer during CMP in preparation for their mechanical removal. The slurry also contains a polishing agent, such as alumina or silica that is used as the abrasive material for the physical removal of the etched/oxidized material. The combination of chemical and mechanical removal of material during polishing results in superior planarization of the polished surface. In this process it is important to remove a sufficient amount of material to provide a smooth surface, without removing an excessive amount of underlying materials at each level of the manufacturing process to insure uniform and accurate formation of the semiconductor device at all subsequent levels. Accurate material removal is particularly important in today's sub-quarter micron technologies where it is critical to minimize thickness variation because the metal lines are getting thinner.

The carrier head provides a controllable load, i.e., pressure, on the wafer to push it against the polishing pad. Some carrier heads include a flexible membrane that provides a mounting surface for the wafer, and a retaining ring to hold the membrane to the mounting surface. Pressurization or evacuation of a chamber behind the flexible membrane controls the load on the wafer. In addition to securing the membrane, the retainer ring acts as a wear surface to assist in the controlled polishing of the wafer. The retainer ring is secured to the periphery of the carrier which secures the edges of the membrane. Such retainer rings are typically secured either through the use of screws or an adhesive. The screw method and adhesive method of attaching the ring to the carrier tends to create uneven wear. Screwing the ring down tends to buckle the ring slightly. As for the adhesive method, it is very difficult to apply the adhesive evenly, which causes slight raises or dips in the ring. If the retainer ring does not seat on the polishing pad evenly, this can cause undesired stresses on the wafer.

SUMMARY

According to one aspect, the subject invention pertains to a wafer carrier pad comprising a membrane secured to the carrier by a retainer ring, wherein the retainer ring is engaged to the carrier without screws or adhesive. Of particular interest is a retainer ring configured such that it engages the carrier by a friction fit or snap fit. In another embodiment, the subject invention pertains to a retainer ring for engaging to the periphery of a carrier for transporting and holding a wafer, said carrier having a front surface and a back surface and a side surface disposed between said front and back surfaces. The retainer ring comprises a first portion sized for extending from the periphery of the carrier to a distance toward the center of the carrier sufficient for holding a membrane. Attached to or integrated with the first portion is a second portion extending transverse to an axis of the first portion. The second portion is sized to span at least a portion of the length of the side surface of the carrier. The second portion comprises an inner wall which abuts against the side surface, and defined on the inner wall is a raised structure. As the retainer ring is engaged to the carrier, the at least one raised structure fits into at least one receptacle defined in the carrier. In a specific aspect, the receptacle is defined in the side surface of the carrier, including at the location where the side and back surfaces meet.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a side perspective view of a carrier embodiment comprising a membrane secured with a retainer ring snap fitted to the carrier.

FIG. 2 shows a cross-sectional view of the embodiment shown in FIG. 1 along the M axis.

DETAILED DESCRIPTION

Reference is made to FIGS. 1 and 2. FIG. 1 shows a perspective side view of a carrier embodiment 100 according to the subject invention. FIG. 2 shows a cross-section of the carrier embodiment 100 along axis AA. The carrier 100 comprises a carrier body 108 which serves as the primary support for the other components of the carrier 100. A membrane 112 is disposed on a front surface 106 of the carrier. In the embodiment shown, pressure under the membrane 112 may be controlled by applying air or vacuum to the chamber 114. As described above, the level of polishing of a wafer (not shown) positioned onto the membrane 112 may be controlled by applying pressure under the membrane 112, which serves to push the wafer (not shown) against a polishing pad (not shown). Air is delivered or removed through the portal 116 which is in fluid communication with the chamber 114. As mentioned, a vacuum may also be applied to the chamber 114. The membrane 112 may comprise one or more small holes (not shown). When a vacuum is applied to the chamber 114 under the membrane 112, the wafer is held against the membrane by the vacuum applied through such holes in accordance with conventional methods.

The membrane 112 is secured to the front surface 106 of the carrier body 108 by employing a ring-shaped retainer ring 110 engaged to the periphery of the carrier body 108. The retainer ring 110 comprises a first portion 111 configured and sized to lay upon the periphery of the front surface 106 such that the edge 113 of the membrane 112 is held under the first portion 111. Attached to or integrated with the first portion 111 is a second portion 115 configured and sized to span a portion of the side surface 117 of the carrier body 108. The cross section of the first and second portions 111,115 is generally L-shaped.

The second portion 115 comprises a raised structure 118 defined on its inward side 119 which is configured to fit into a receptacle 120 defined on the side surface 117. In the embodiment shown in FIG. 2, the receptacle is defined at the junction between the side surface 117 and the back surface 104 of the carrier body 108. The raised structure 118 catches or snaps into the receptacle 120 to securely fasten the retainer ring 110 to the carrier body 108. It should be noted that in alternative embodiments the side surface comprises a raised structure and the second portion comprises a receptacle into which the raised structure fits; or the second portion and side surface may both comprise interlocking raised features. Those skilled in the art will appreciate that other snap fit or friction fit mechanisms for securing the retainer ring 110 to the carrier body 108 may be implemented. For example, clasp configurations, tongue and groove configurations with or without clasp configurations and many other configurations could be adapted for securing the retainer ring to the carrier body 108 that do not need screws or adhesives for secure engagement.

While the preferred embodiments of the present invention have been shown and described herein in the present context, it will be obvious that such embodiments are provided by way of example only and not of limitation. Numerous variations, changes and substitutions will occur to those of skilled in the art without departing from the invention herein. For example, the present invention need not be limited to best mode disclosed herein, since other applications can equally benefit from the teachings of the present invention. Accordingly, it is intended that the invention be limited only by the spirit and scope of the appended claims. 

1. A carrier for use with an integrated circuit wafer comprising: a carrier body comprising a front surface, a back surface and a side surface; a retainer ring comprising a first portion sized and configured for positioning on a portion of said front surface and having a second portion attached to or integrated with said first portion, said second portion comprising an inner surface sized and configured for positioning on all or a portion of said side surface; a snap fit mechanism defined on said inner surface and said side surface for securing said retainer ring to said carrier body; and a membrane covering a portion of said front surface and secured to said carrier body by said retainer ring.
 2. The carrier of claim 1, wherein said snap fit mechanism comprises a raised structure defined on said inner surface and a receptacle defined on said side surface into which said raised structure fits.
 3. The carrier of claim 1, wherein said snap fit mechanism comprises a raised structure defined on said side surface and a receptacle defined on said inner surface into which said raised structure fits.
 4. The carrier of claim 1, wherein said retainer ring and said carrier body comprise an annular dimension.
 5. The carrier of claim 1, wherein said retainer ring is secured to said carrier body without the need for employing screws or an adhesive.
 6. The carrier of claim 1, wherein a cross-section of said retainer ring depicts an L-shaped structure.
 7. The carrier of claim 1, wherein said first portion comprises an axis that is transverse to an axis of said second portion.
 8. The carrier of claim 7, wherein said first portion is perpendicular to said second portion.
 9. The carrier of claim 1, wherein said front surface and said back surface is circular and wherein said retainer ring is ring-shaped.
 10. The carrier of claim 1, wherein said carrier body comprises a portal to deliver and remove air from a space defined between said membrane and said front surface.
 11. The carrier of claim 1, wherein said membrane comprises an outer edge onto which said front portion applies force to secure said membrane to said carrier body.
 12. A carrier for use with an integrated circuit wafer comprising: a carrier body comprising a front surface, a back surface and a side surface; a retainer ring comprising a first portion sized and configured for positioning on a portion of said front surface and having a second portion attached to or integrated with said first portion, said second portion comprising an inner surface sized and configured for positioning on all or a portion of said side surface, wherein said second portion is engaged to said side surface; and a membrane covering a portion of said front surface and secured to said carrier body by said retainer ring. 